New guidance on relationships and sex education has led to fears that the Government is undermining the rights of parents.
Education secretary Damian Hinds announced the guidance this week on new compulsory RSE lessons coming into effect across England's schools in September 2020.
Controversially, the new guidance sets limits on the extent to which parents can withdraw their children from the the lessons, which will cover topics like transgenderism, homosexuality and relationships.
Headteachers can approve parents' opt out requests until children reach the age of 15 but may decline to do so in 'exceptional circumstances'. After this time, the children can decide for themselves if they would like to opt in to the sex education lessons.
Parents of primary school children will have no opt out right for the relationships education classes, which will teach about the diversity of relationships and family set-ups in modern Britain.
The Society for the Protection of Unborn Children said the Government was trampling on the rights of parents.
Antonia Tully, who heads up SPUC's Safe at School campaign said: 'Parents are increasingly concerned as the Government seems determined to trample over their rights to bring up their children in line with their own values.'
The Safe at School campaign has sent thousands of postcards to the Secretary of State demanding a U-turn on the plans, which will end the decades-long right to opt-out.
'We will be analysing the new draft guidance carefully and alerting supporters as to the next steps,' Mrs Tully added.
Mr Hinds was challenged on the guidance during a debate held in the House of Commons this week in response to over 100,000 people signing a petition demanding that the right to opt out be retained.
Sir Edward Leigh said: 'All previous Conservative Governments have given an untrammelled right to parents to remove their children from sex education.
'But here in certain circumstances that right has been transferred to the headteacher. A fundamental shift of power to the state.'
Shabana Mahmood, the Labour MP for Birmingham, Ladywood, said some schools were flouting the legal requirement to consult with parents on the content of RSE lessons.
'Everybody feels it is okay to ride roughshod over orthodox communities and push them to one side,' she said.
Parents of children attending Parkfield Community School in Birmingham have been particularly vocal in their opposition to lessons teaching children about gender and homosexuality.
Over 300 Muslim and Christian parents have protested at the school gates in recent weeks to challenge the lessons.
